@blockly/plugin-scroll-options Built on Blockly

A Blockly plugin that adds additional scroll features.

This plugin adds two features related to scrolling:

  • Users can scroll the workspace with the mousewheel while dragging a block ("wheel scroll").
  • The workspace will automatically scroll when a block is dragged near the edge of the workspace ("edge scroll").

Each of these options can be enabled or disabled independently, if you only want one of these behaviors. The edge scrolling behavior can also be configured with options such as fast and slow scroll speeds and the distance from the edge of the workspace that the block should be before autoscrolling is activated. See the Usage and API sections for more details on how to configure these behaviors.



yarn add @blockly/plugin-scroll-options


npm install @blockly/plugin-scroll-options --save


Basic usage. If you don't pass any options to init, then you will get the default behavior, which enables both scroll options and uses the default parameters for edge scrolling.

import * as Blockly from 'blockly';
import {
} from '@blockly/plugin-scroll-options';

// Inject Blockly.
const workspace = Blockly.inject('blocklyDiv', {
  toolbox: toolboxCategories,
  plugins: {
    // These are both required.
    blockDragger: ScrollBlockDragger,
    metricsManager: ScrollMetricsManager,
  move: {
    wheel: true, // Required for wheel scroll to work.

// Initialize plugin.
const plugin = new ScrollOptions(workspace);

If you want to disable one (or both) behaviors from the start, you can pass options to init.

plugin.init({enableWheelScroll: false, enableEdgeScroll: false});

If you want to supply custom configuration to the edge scrolling behavior, you can also pass in that option to init.

plugin.init({edgeScrollOptions: {slowBlockSpeed: 0.1}});

This can be combined with the previous example to disable wheel scroll at the same time. For more details on the edge scroll options, see the next section.


The plugin is configured during initialization for convenience. It can also be configured, or reconfigured, at any time afterwards using the following methods on ScrollOptions:

  • enableWheelScroll/disableWheelScroll
  • enableEdgeScroll/disableEdgeScroll
  • updateEdgeScrollOptions

IMPORTANT: Currently, the options to configure the edge scroll behavior are provided statically due to the way a BlockDragger is initialized. Thus, each instance of the plugin will share the same settings, even if you call updateEdgeScrollOptions on different instances of the plugin (i.e., on different workspaces). You can have some workspaces using the plugin and some not, but any that are using the plugin will share the settings. If this is a blocking issue for you, please file an issue on blockly-samples.

The edge scroll options are provided in an object with the following properties (default values in parentheses):

  • slowBlockSpeed (0.28), fastBlockSpeed (1.4): Pixels per ms to scroll based on how far the block is from the edge of the viewport.
  • slowBlockStartDistance (0): Distance in workspace units that the edge of the block is from the edge of the viewport before the corresponding scroll speed will be used. Can be negative to start scrolling before the block extends over the edge.
  • fastBlockStartDistance (50): Same as above, for fast speed. Must be larger than slowBlockStartDistance.
  • oversizeBlockThreshold (0.85): If a block takes up this percentage of the viewport or more, it will be considered oversized. Rather than using the block edge, we use the mouse cursor plus the given margin size to activate block-based scrolling.
  • oversizeBlockMargin (15): Cursor margin to use for oversized blocks. A bigger value will cause the workspace to scroll sooner, i.e., the mouse can be further inward from the edge when scrolling begins.
  • slowMouseSpeed (0.5), fastMouseSpeed (1.6): Pixels per ms to scroll based on how far the mouse is from the edge of the viewport.
  • slowMouseStartDistance (0): Distance in workspace units that the mouse is from the edge of the viewport before the corresponding scroll speed will be used. Can be negative to start scrolling before the mouse extends over the edge.
  • fastMouseStartDistance (35): Same as above, for fast speed. Must be larger than slowMouseStartDistance.

Each of these options is configured with the default value shown, which is specified in ScrollBlockDragger.js. When you call updateEdgeScrollOptions, only the properties actually included in the options parameter will be set. Any unspecified options will use the previously set value (where the initial value is from the default options). Therefore, do not pass in any options with explicit undefined or null values. The plugin will break. Just leave them out of the object if you don't want to change the default value.

This method is safe to call multiple times. Subsequent calls will add onto previous calls, not completely overwrite them. That is, if you call this with:

updateEdgeScrollOptions({fastMouseSpeed: 5});
updateEdgeScrollOptions({slowMouseSpeed: 2});

Then the final options used will include both fastMouseSpeed: 5 and slowMouseSpeed: 2 with all other options being the default values.

You can call ScrollBlockDragger.resetOptions() to restore all default options.


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